1. Field of the Invention
The present invention relates to a pager provided with display function to display certain messages, and particularly relates to a pager provided with a function to enable or disable display of messages and to change the display contrast according to the ambient environment.
2. Description of the Related Art
In general, a pager with display function to display certain messages is provided with a liquid crystal display (LCD) for a smaller size and a lighter weight. However, the visibility of the LCD display screen largely varies depending on the ambient brightness and it is difficult to read the displayed message in a dark place. Therefore, there have been many proposals about display of messages in a dark place.
According to some examples of such proposals, the pager may be automatically switched between the display mode and the no-display mode for the display screen according to the ambient brightness, or the display on the display unit may be turned on and off by switch operation. Conventional inventions of this type include Japanese Patent Application Laid-open (kokai) No. Heisei 6-237206 "RADIO PAGER AND ITS CONTROL METHOD", Japanese Patent Application Laid-open (kokai) No. Heisei 5-167506 "PAGER", Japanese Patent Application Laid-open (kokai) No. Heisei 4-306023 "PAGER", and Japanese Patent Application Laid-open (kokai) No. Heisei 3-7433 "RADIO PAGER".
Japanese Patent Application Laid-open No. Heisei 6-237260 "RADIO PAGER AND ITS CONTROL METHOD" discloses a pager provided with a photo sensor to detect the brightness of the message display environment. When a pager call is stopped in a dark environment, this pager stores the received message as an unread message so that the user can read that message in a bright place later. Besides, when the pager detects that the ambient environment around the pager changes from a dark condition to a bright condition, it notifies the user of any unread message stored as described above.
Japanese Patent Application Laid-open No. Heisei 5-167506 "PAGER" discloses a pager provided with a light receiver to detect the brightness around the pager and a control circuit to turn off the message display upon detection of a dark condition by the light receiver when the pager is in the wait or new receipt status. While this pager is displaying that it is in the wait or new receipt status, it turns off the display when it is in a dark place and turns on the display only when it is in a bright place.
According to Japanese Patent Application Laid-open No. Heisei 4-306023 "PAGER", a pager comprises an illumination means to illuminate the display means and a display control means. This display control means causes the display means to display the time data upon switch operation while the pager is waiting for a call and then reads the received message data so that it is displayed on the display means. When it is dark around the pager, this pager has the above illumination means illuminate the above display means during display of the time data and the received message data.
Japanese Patent Application Laid-open No. Heisei 3-7433 "RADIO PAGER" discloses a pager comprising a light detection means to detect the ambient light intensity, a control means to disable displaying on the display means when the light quantity detected by the light detection means is below a certain standard and a light source control means to control the intensity of the light source to illuminate the display means.
Among other conventional inventions, there have been proposals to illuminate the LCD with a back light when it is dark around the pager. Conventional inventions of this type include Japanese Patent Application Laid-open No. Heisei 5-122129 "RADIO PAGER", Japanese Patent Application Laid-open No. Heisei 4-306023 "PAGER", Japanese Patent Application Laid-open No. Heisei 3-268628 "RADIO PAGER WITH DISPLAY FUNCTION", and Japanese Patent Publication No. Heisei 3-29328 "RADIO PAGER WITH DISPLAY".
According to Japanese Patent Application Laid-open No. Heisei 5-122129 "RADIO PAGER", a pager sends the operation signal from the decoder to the driving circuit when informing the receipt of a message to cause the double duty lighting means to emit the light. When displaying a message in a dark place, this pager sends the operation signal from the photo sensor circuit to the driving circuit to turn on the double duty lighting means for illumination of the display unit and controls the light intensity of the double duty lighting means by switching the frequency of the operation signal between the receipt information mode and the display unit illumination mode.
Japanese Patent Application Laid-open No. Heisei 4-306023 "PAGER" discloses a pager comprising an illumination means to illuminate the display means and a display control means. Upon switch operation while the pager is waiting for a call, the above display control means causes the display means to display the time data on the display means, reads the received message data so that it is displayed on the display means, and has the above illumination means illuminate the above display means during display of the time and received message data.
Japanese Patent Application Laid-open No. Heisei 3-268628 "RADIO PAGER WITH DISPLAY FUNCTION" discloses a pager which illuminates the display means with the illumination means when the display means is in the received data display status and the light quantity around the display means is below a certain level and also illuminates the display means with the illumination means when the display means is in the general data display status and the light quantity around the display means is below a certain level and an illumination instruction given by switch operation is detected.
Japanese Patent Publication No. Heisei 3-29328 "RADIO PAGER WITH DISPLAY" discloses a pager comprising a data processing means, a display unit, a light detection means to detect that the light quantity around the display unit is below a predetermined level and outputs the detection signal to the data processing means and a display unit illumination circuit having an illumination lamp to illuminate the display unit according to the control signal from the data processing means. The above data processing means comprises a means to generate the control signal when it detects that the output from the detection means is below a predetermined level while the pager is in the display reading status; the above detection means comprises a means to detect that the light quantity is not less than the second predetermined level, which is higher than the above predetermined level, and to send the detection signal to the data processing means so that the above illumination lamp is turned off by such detection signal.
The conventional pagers above have, however, the same light intensity for the LCD. Therefore, the message on the LCD is not displayed in a sharp contrast with the light received by the LCD in some optical environment. This may make it difficult to read the displayed message or may provide excessive light intensity to the LCD, resulting in meaningless quick consumption of the battery.